The USDA has given more than $450,000 for a research project designed to increase the safety of certain commercially farmed oysters from the Gulf Coast that are “bound for the premium half-shell market.”

A marine scientist at Auburn University, Bill Walton, is known as one of the driving forces behind the Gulf Coast’s up-and-coming, off-bottom oyster industry, according to a news release from the school’s College of Agriculture.

“Through his project, Walton should generate valuable data for Gulf Coast oyster farmers, who focus on producing exceptional oysters for high-end markets, such as upscale restaurants that offer the farmed bivalve mollusks on the half shell,” the school reported.

The grant for Walton’s work is one of 13 competitive food safety awards that USDA’s National Institute for Food and Agriculture has announced as part of its Agriculture and Food Research Initiative. It will fund a three-year study to determine whether an oyster farm’s geographic location, handling practices, and choice of equipment affect Vibrio levels in farm-raised oysters.

Vibrio are bacteria that occur naturally in warm ocean waters, such as the Gulf of Mexico. Certain Vibrio species, most notably Vibrio vulnificus, can cause foodborne illnesses in people who eat raw or undercooked shellfish.

According to the Centers for Disease Control about 80,000 people get sick with vibriosis each year in the United States. About 52,000 of these illnesses are the result of eating contaminated food, primarily raw or undercooked shellfish, particularly oysters. Non-foodborne vibriosis cases usually involve someone with an open wound swimming or wading in brackish or saltwater where there are dangerous levels of Vibrio.

Depending on the specific type of vibrio involved, there is up to a 25 percent fatality rate among people who are infected.

“Our findings will help farmers understand and manage their preharvest production techniques to minimize the risk of foodborne illness in consumers,” said Walton, who is an associate professor in Auburn’s School of Fisheries, Aquaculture and Aquatic Sciences and a marine aquaculture specialist with the Alabama Cooperative Extension System.

Upscale restaurants have higher standards that many other fresh oyster buyers, and those standards mean oyster farmers can charge higher prices. To secure a piece of the action, commercial oyster farms have developed “off-bottom” practices. 

One of those practices is a double-edged sword, though. It improves the overall quality of the shellfish, but can decrease food safety.

“To achieve the superior product the market demands, farmers grow their oysters in underwater baskets or cages that float above the ocean floor. Once a week, they raise the baskets out of the water and allow the oysters to air-dry. That practice prevents barnacles, seaweed and other undesirable organisms from attaching to and marring the oysters,” according to the release from Auburn University.

The frequent handling exposes the oysters to elevated air temperatures and also interrupts filter feeding. Both factors cause Vibrio levels to rise in the oysters’ flesh.

“In our trials, we will look at how long after the oysters are resubmerged the Vibrio levels return to naturally occurring levels,” he said. “Our results will help farmers as they evaluate their production techniques.”

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